An axial gas turbine engine, such as an aircraft “jet-engine”, generally comprises an air inlet, a compressor section, a fuel combustion chamber, a turbine section, one or several rotatable drive shafts connecting corresponding compressors and turbines, an exhaust outlet and structures for supporting the drive shafts and for mounting the engine to e.g. an aircraft.
Typically, the supporting structures are static parts that include an inner shell or ring, for connection to bearings and a centrally located drive shaft, and an outer shell or ring, for connection to e.g. an engine casing, and where circumferentially distributed elements (struts, vanes) extend between and connect the inner and outer shells/rings. The supporting structures are designed to be capable of transferring loads between the drive shaft and the engine casing. An axial gas flow through the engine is allowed to flow between the elements which normally are aerodynamically designed. Supporting structures of the type discussed here are exposed to rather extreme balance loads and thermally generated loads.
The part of the supporting structure positioned inside of the inner ring, i.e. the part that transfer loads between the shaft bearing seats and the inner ring, includes normally an annular load transferring wall-shaped structure that is fastened to an inner side of the inner ring and that extends inwards in a radial direction towards the shaft bearings. Typically, this annular load transferring structure extends both radially and axially as to form a cone-shaped member, such as the bearing cones shown in US 2008/134688 and US 2008/022692.
Different designs of inner load transferring structures are known and these can be divided into open and closed structures, where the term “open” refers to the possibility to allow for inspection (to detect damages etc.). A conventional bearing cone normally forms an open structure that can be inspected from both sides. EP 1482130 shows an example of an at least partly closed structure. Closed structures can more easily be designed to withstand high loads but since the possibility of inspecting load-carrying parts is highly desired, in particular in aircraft applications, open structures are generally preferred. In aircraft applications it is also important to reduce the weight of the structures used.
Another known open annular load transferring structure comprises first and second parallel annular beam elements that are connected to the inner side of the inner ring at an axial distance from each other. The forward/upstream annular beam is in turn connected to the shaft bearing seat. A number of circumferentially distributed ribs are provided that connect the two annular beam elements for the purpose of preventing them from being bent in an axial direction and thus retaining the shape of the elements. In many cases this open structure works well but it has been discovered that in some applications this design leads to very high local stresses that may affect the durability of the entire supporting structure.
There is still a need for improvements regarding inner annular structures of the above type, in particular there is a need to lower the weight and to improve the durability.